Synchronous-rectification type control for direct current motors and method of making

Abstract

A MOSFET control topology and a physical structure for a motor control which provide a more efficient and economic DC motor control are disclosed. The control topology introduces a synchronous-rectification technique wherein free-wheel diodes are replaced with MOSFET devices that are switched on and off by a logic circuit so that they are conductive for commuting motor current during periods that the motor current supply is switched off. The physical structure and method of assembling a DC motor control eliminate time consuming assembly techniques while ensuring effective waste heat exchange between electronic components and a heat sink of the control by providing quick-install spring retainers for urging the components into heat sink conducting contact with the heat sink. The physical structure also provides for high density packing of electronic components in a controller.

We claim: 
     
       1. An electronic control for a direct current traction motor, comprising: a first plurality of parallel-connected power field effect transistors arranged for connection in series with the motor, a field gate electrode of each first field effect transistor being connected to a first common control line for controlling an on-off cycle of conduction through the first field effect transistors to provide drive current to the motor from a direct current source; and   a second plurality of parallel-connected power field effect transistors arranged for connection in parallel with the motor, a field gate electrode of each second field effect transistor being connected to a second common control line for controlling a synchronous-rectification on-off cycle of conduction through the second field effect transistors in synchronism with the on-off cycle of conduction of the first field effect transistors for commuting a motor current when the first parallel-connected field effect transistors are switched off.   
     
     
       2. The electronic control as claimed in claim 1, further including a microprocessor and a control logic circuit driven by the microprocessor, the control logic circuit having first and second discrete output lines which are in respective electrical connection with the first and second common control lines. 
     
     
       3. The electronic control as claimed in claim 2, wherein the microprocessor outputs two separate signals to the control logic circuit, a pulse width modulated on/off motor current regulation command signal and an enable signal to ensure that both the first and second plurality of power field effect transistors are switched off if a fault condition is detected. 
     
     
       4. The electronic control as claimed in claim 3, wherein: the control logic circuit includes a first phase inverter, a pulse delay circuit, a second phase inverter, first and second electrical AND gates and first and second drive circuits in electrical connection with the first and second discrete output lines. 
     
     
       5. The electronic control as claimed in claim 4 wherein the pulse delay circuit delays the pulse width modulated on/off motor current regulation command signal for a period of time that exceeds a device switch time of the first and second plurality of field effect transistors. 
     
     
       6. The electronic control as claimed in claim 3, wherein the pulse-width modulated on/off motor current regulation signal is cycled at a frequency of at least 15,000 Hz so that the control does not emit noise in an audible range for humans. 
     
     
       7. The electronic control as claimed in claim 1, further including at least one plug braking diode connected in parallel with an armature of the motor to commute armature current when a polarity of a field of the motor is reversed in order to brake a momentum of equipment driven by the motor. 
     
     
       8. The electronic control as claimed in claim 1, further including at least one low resistance, low inductance capacitor connected in parallel with a battery for providing the direct current supply, said capacitor having a capacitance adequate to even a load on the battery to an extent that the load is substantially constant. 
     
     
       9. An electronic control for a direct current traction motor, comprising: a first plurality of parallel-connected power field effect transistors arranged for connection in series with the motor, a field gate electrode of each first field effect transistor being connected to a first common control line;   a second plurality of parallel-connected power field effect transistors arranged for connection in parallel with the motor, a field gate electrode of each second field effect transistor being connected to a second common control line; and   control circuitry for generating first and second synchronous control signals, the control circuitry being connected to the first common control line which conducts the first control signal to switch the first field effect transistors in an on-off cycle of conduction to provide drive current to the motor from a direct current source, and the control circuitry being connected to the second common control line which conducts the second control signal for switching the second field effect transistors in a synchronous-rectification cycle of conduction for commuting a motor current when the first field effect transistors are switched off.   
     
     
       10. The electronic control for a direct current traction motor as claimed in claim 9 wherein the control circuitry includes a signal delay circuit, and the control circuitry generates the first and second control signals from a single pulse width modulated input signal, the first control signal corresponding in phase and duration to the pulse width modulated input signal and the second control signal being inverted in phase and delayed with respect to the first control signal so that the first and second plurality of field effect transistors are not simultaneously conductive. 
     
     
       11. The electronic control for direct current traction motor as claimed in claim 10 wherein the control circuitry further includes an enable signal input terminal and the control circuitry drives the first and second control signals low to turn off both the first and second plurality of field effect transistors when an enable signal applied to the input terminal is driven low, regardless of a state of the pulse width modulated input signal. 
     
     
       12. The electronic control for a direct current traction motor as claimed in claim 11 wherein the electronic control further includes a microprocessor generating the pulse width modulated signal and the enable signal.